Bacteria of the Mycoplasma genus belong to the class Mollicutes and represent a group of organisms that derived from the Firmicutes lineage. Mollicutes are the smallest autonomously replicating organisms, which differ structurally from other eubacteria in that they lack a cell wall. The surface of their single membrane is considered a key interface in mediating adaptation and survival in the context of a complex, immunocompetent host. Further, Mollicutes have a small genome and a limited number of metabolic pathways. Therefore, members of the Mycoplasma genus have also been portrayed as “minimal self-replicating organisms.” However, despite this apparent simplicity, a large number of mycoplasma bacteria are pathogens of humans and a wide range of animals. In contrast to other pathogenic bacteria where virulence is mostly determined by toxins, invasins, and cytolysins, pathogenic Mycoplasma bacteria appear to have no such typical primary virulence factors (Chambaud, I. et al, 2001, Nucleic Acids Res. 29: 2145-2153, Fraser et al, 1995, Science 270: 397-403). There is currently little knowledge available on the molecular mechanisms and the effectors that allow pathogenic mycoplasmas to cause host cell damage, inflammation and disease.
Pathogenic Mycoplasma bacteria cause mainly atypical pneumonia, uro-genital infections and arthritis in humans and in animals (Blanchard, A., and G. F. Browning (eds.). 2005. Mycoplasmas: Molecular biology, pathogenicity and strategies for control. Horizon Bioscience, Wymondham U. K.; Kobisch M. and Friis N. F. 1996, Swine mycoplasmoses, Rev. Sci. Tech. Off. Int. Epiz. 15, 1569-1605). It is known that reactivation or exacerbation of the signs repeats and transfers gradually to a chronic disease, and thus along with early diagnosis and early treatment, prevention or treatment of exacerbation or reactivation are important. M. hyopneumoniae is the aetiological agent of enzootic pneumonia. In swine it is one of the most common and economically important diseases due to reduced weight gain and poor feed efficiency. The disease causes lesions in the lungs, a chronic cough, dull hair coat, retarded growth and unthrifty appearance lasting several weeks. The lung lesions, particularly in ventral apical and cardiac lobes, are characterized by a hyperplasia of the epithelial cells and an increased perivascular and peribronchiolar accumulation of mononuclear cells. M. hyorhinis, another common mycoplasma of the respiratory tract of pigs, can cause polyserositis and arthritis in piglets. M. hyosynoviae is generally located in the tonsils and can cause arthritic disease, leading to economic losses. M. hyosynoviae is isolated from the joints and pharyngeal/tonsillar samples and can induce antibodies in blood and joint fluid. M. bovis is considered to be one of the more pathogenic bacteria of Mycoplasma and causes significant economic losses worldwide. Mycoplasma bacteria cause severe clinical signs in cattle of all ages. M. bovis is the most frequent Mycoplasma pathogen found to cause pneumonia, mastitis, and arthritis in cattle and its etiological role has also been associated with otitis, keratoconjunctivitis, synovitis, and reproductive disorders in cows and bulls.
Because mycoplasma lack a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. Therapeutic agents for mycoplasma infection that are in practical use are some antibiotics such as macrolide-based, or new quinolone-based, or tetracycline-based antibiotics, but such antibiotics have great adverse effects such as advent of drug-resistant strains, which leads the mycoplasma infection to become severe while sufficient treating effects are not expected, and becomes a cause for transfer to a chronic disease. Further, vaccination is an effective method of controlling mycoplasma infection. However, significant high yields of mycoplasma needed for the preparation of vaccines are obtained by cultivation normally only in complex media (Kobisch M. and Friis N. F. 1996, Swine mycoplasmoses, Rev. Sci. Tech. Off. Int. Epiz. 15, 1569-1605; Gabridge M. G. et al. 1976, Cultivation of mycoplasma in a modified tissue culture medium, Applied and Environmental microbiology. 31, 986-989; Sotoodehnia A. Et al 2007, Preparation of agalactia vaccine in fermentor, Archives of rani institute, 62, 45-48; Dahlia et al., 2009 Isolation of Mycoplasma hyosynoviae from pneumonic lung of swine, Tropical Biomedicine 26:341-345). Dependent on the mycoplasma bacteria to be cultivated, the complex media are supplemented with 10-30% serum and sometimes with yeast extract. Thus, due to the high price of serum the cultivation of mycoplasma bacteria is cost intensive. Further, a reduction of serum in the complex media would be beneficial in light of animal welfare, too. Thus, there is a need for the cultivation of significant high yields of mycoplasma in a serum-reduced culturing system for the preparation of immunogenic compositions effective in preventing mycoplasma infection. Moreover, the swine specific mycoplasma bacteria are generally cultivated in complex media containing swine specific serum (Kobisch M. and Friis N. F. 1996, Swine mycoplasmoses, Rev. Sci. Tech. Off. Int. Epiz. 15, 1569-1605). However, swine specific serum can contain other swine-specific pathogens or can contain antibodies against swine specific pathogens which can cause a reduced immunogenicity of the immunogenic composition to be prepared. Thus, there is also a need for the cultivation of significant high yields of mycoplasma in a swine serum-free culturing system for the preparation of immunogenic compositions effective in preventing mycoplasma infection.